It will haunt Gordon Brown for ever: the moment he described Rochdale pensioner Gillian Duffy as bigoted while unwittingly still being recorded on an open microphone as he was driven away.

But what happened after the microphone went dead?

The Guardian has been told that Brown became aware within seconds that the Sky News mike clipped to his lapel was still on.

The then prime minister immediately realised the scale of the disaster, but he was twice assured by his press officer, Iain Bundred, that his remarks would not be broadcast since there was an understanding with the broadcasters that they would only use his remarks with his agreement.

Brown apparently knew the story was too big to be suppressed, and that he had blown his efforts to reconnect with so-called C2 voters.

It has also been revealed that he knew he was being filmed in the fateful Radio 2 interview with Jeremy Vine, soon after the incident, including the moment he was seen slumped in a chair, hand on forehead, as his words were played back to him live.

His team had apparently been surprised that the playback was left to the end of the programme.

Brown's team also now regrets that he left Downing Street on the Saturday after the indecisive general election to go to Scotland. He departed for his constituency to minimise suggestions that he was squatting in Downing Street.

It is thought that if he had stayed in London he could have done more to rally the parliamentary party and cabinet to the idea of trying to form a progressive government with the Liberal Democrats.